Abstract:

We used extreme pedal rates to investigate the influence of muscle fibre recruitment on pulmonary VO2 kinetics during unloaded-to-moderate-intensity (U → M), unloaded-to-high-intensity (U → H), and moderate-intensity to high-intensity (M → H) cycling transitions. Seven healthy men completed transitions to 60% of the difference between gas-exchange threshold and peak VO2 from both an unloaded and a moderate-intensity (95% GET) baseline at cadences of 35 and 115 rpm. Pulmonary gas exchange was measured breath-by-breath and iEMG of the m. vastus lateralis and m. gluteus maximus was measured during all tests. At 35 rpm, the phase II time constant (τp) values for U → M, U → H, and M → H were 26 ± 7, 31 ± 7 and 36 ± 8 s with the value for M → H being longer than for U → M (P <0.05). At 115 rpm, the τp values for U → M, U → H, and M → H were 29 ± 8, 48 ± 16 and 53 ± 20 s with the value for U → M being shorter than for the other two conditions (P <0.05). The VO2 slow component was similar at both cadences, but iEMG only increased beyond minute 2 during high-intensity cycling at 115 rpm. These results demonstrate that VO2 kinetics are influenced by an interaction of exercise intensity and pedal rate and are consistent with the notion that changes in muscle fibre recruitment are responsible for slower phase II VO2 kinetics during high-intensity and work-to-work exercise transitions.

Description:

DiMenna F.J., Wilkerson, D.P., Burnley, M., Bailey, S.J. &amp; Jones, A.M. (2009). Influence of extreme pedal rates on pulmonary O2 uptake kinetics during transitions to high-intensity exercise from an elevated baseline. Respiration Physiology and Neurobiology, 169, 16-23. This paper demonstrated that both exercise intensity and muscle contractile frequency can influence the kinetics of . Specifically, at low contraction frequencies, the influence of transitions to moderate vs. heavy exercise was blunted, whereas they were amplified at high contraction frequencies. When the transition occurred from an elevated (moderate) baseline, the same effect was seen, suggesting that the interpretation of the response is dependent on the contractile frequency adopted.